JPH01321333A - Sample gas analyzer - Google Patents

Abstract

PURPOSE:To enhance analytical accuracy by controlling the pressure of a primary pressure reducing chamber or the opening area of an orifice so that the flow rate of the sample gas introduced into a secondary reducing chamber from the primary pressure reducing chamber through the orifice becomes almost constant. CONSTITUTION:When an analysis start signal is inputted to a drive control part C1, the control part C1 operates vacuum pumps 11, 21 to respectively reduce the pressures of primary and secondary pressure reducing chambers 5, 15. Next, the control part C1 drives a solenoid 7 for a predetermined time during the exhaust process of an engine 2 after the vacuum degrees of the pressure reducing chamber 5, 15 reach respective set values to open a control valve 6. By this method, the exhaust gas in a combustion chamber 3 is introduced into the pressure reducing chamber 5 through an introducing pipe 4. At this time, the control part C1 keeps the vacuum degree of the pressure reducing chamber 5 constant on the basis of the pressure signal of a pressure sensor 10. Therefore, the difference between the vacuum degrees of the pressure reducing chambers 5, 15 during analysis becomes almost constant and, when analysis is performed by a quadrupole mass detector 8, an ionizing degree becomes almost constant and the ion mass of a specific gaseous component can be analyzed with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a sample gas analyzer, and in particular, a sample gas is introduced from a primary vacuum chamber through an orifice into a secondary vacuum chamber equipped with a quadrupole mass detector. This relates to a device in which the gas flow rate of sample gas is kept approximately constant.

[Prior art]

Generally, a sample gas analyzer for analyzing chemical substances contained in gas, for example, has a primary vacuum chamber into which the sample gas is introduced, and a quadrupole mass that communicates with this primary vacuum chamber via an orifice or the like. A secondary decompression chamber equipped with a detector is provided, and the sample gas introduced into the primary decompression chamber is introduced into the secondary decompression chamber with its gas flow rate regulated by an orifice, and the sample gas is detected by a quadrupole mass detector. A device is known that selectively detects the mass of a specific gas component therein.

The gas analyzer is suitable for analyzing intake gas, combustion gas, exhaust gas, etc. of an automobile engine, and is configured as shown in FIG. 6, for example.

In this gas analyzer, a primary decompression chamber 50 and a secondary decompression chamber 51 are provided adjacent to each other, and the secondary decompression chamber 51 communicates with the primary decompression chamber 50 via an orifice 52. is depressurized to a set value by a vacuum pump 53, and the secondary decompression chamber 51 is depressurized to a set value by a turbo molecular pump 54 and a vacuum pump 55. Note that the degree of vacuum in the secondary decompression chamber 51 is set higher than the degree of vacuum in the primary decompression chamber 50 by a predetermined value.

For example, when the engine 56 is in the exhaust process, the control valve 57 is opened, and the exhaust gas (sample gas) in the combustion chamber 58 is
is introduced into the primary decompression chamber 50 via the sample gas introduction pipe 59, and a portion of the sample gas is introduced into the orifice 52 by differential pumping.
It is introduced into the secondary decompression chamber 51 through the passage.

Then, the sample gas is ionized and analyzed by a quadrupole mass detector 60 in the secondary decompression chamber 51 to detect the ion mass of a specific gas component.

In addition, Japanese Utility Model Application Publication No. 58-26660 discloses that when an oxidation catalyst provided in a sample gas introduction tube is heated to approximately 300°C or higher in a heating furnace, and the sample gas is sent through the introduction tube to the primary decompression chamber. After the CO and various HCs in the sample gas are completely oxidized with an oxidation catalyst, they are analyzed with a quadrupole mass detector in the secondary vacuum chamber, and the air-fuel ratio of the mixture is calculated based on the analysis results. An ultrahigh-speed sample gas analyzer is described.

[Problem to be solved by the invention]

In the conventional sample gas analyzer (see FIG. 6), for example, when the exhaust gas (sample gas) of the engine 56 is introduced into the primary decompression chamber 50 through the introduction pipe 59 and analyzed, the primary decompression chamber 50 is Although the degree of vacuum in the decompression chamber 50 and the degree of vacuum in the secondary decompression chamber 51 by the pair of vacuum pumps 54 and 55 are set to be approximately constant, the exhaust gas pressure inside the engine 56 changes from time to time, so the exhaust gas pressure increases. Then, the degree of vacuum in the primary decompression chamber 50 becomes lower due to the introduction of the sample gas, and the difference in the degree of vacuum between the compartments 50 and 51 increases, so that the vacuum level in the primary decompression chamber 50 is reduced through the orifice 52 to the secondary decompression chamber 51. The flow rate of the introduced sample gas increases, and the gas flow rate (introduction amount) passing through the orifice increases.

As a result, the degree of vacuum in the secondary decompression chamber 51 changes greatly, and the gas concentration of the sample gas in the secondary decompression chamber 51 also changes, so depending on the type of gas, the degree of ionization changes depending on the degree of vacuum, and the quadrupole There is a problem in that the mass detector 60 cannot accurately detect the ion mass of the gas component.

Therefore, the degree of vacuum in the secondary decompression chamber 51 is measured, a coefficient for correction is determined from the difference from the predetermined degree of vacuum, and the actual value determined by the quadrupole mass detector 60 is multiplied by the coefficient for correction. However, this correction requires complex arithmetic control, which impedes the speed of gas analysis.For example, the degree of vacuum and degree of ionization have a nonlinear correlation, such as in oxygen There are problems with gas components such as simply correcting them using coefficients, as errors may occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sample gas analyzer that can improve the accuracy of sample gas analysis and perform gas analysis at high speed.

[Means to solve the problem]

The sample gas analyzer according to the present invention includes a primary decompression chamber into which a sample gas introduction pipe is introduced, a secondary decompression chamber communicated with the primary decompression chamber through an orifice, and a secondary decompression chamber provided in the secondary decompression chamber. In a sample gas analyzer equipped with a quadrupole mass detector, the primary depressurization is performed such that the flow rate of the sample gas introduced from the primary decompression chamber to the secondary decompression chamber through the orifice is approximately constant. A gas flow rate control means is provided to control the pressure in the chamber or the opening area of the orifice.

[Effect]

In the sample gas analyzer according to the present invention, when a part of the sample gas introduced into the primary decompression chamber via the sample gas introduction tube is introduced into the secondary decompression chamber via the orifice, The pressure in the primary decompression chamber or the opening area of the orifice is controlled, and the flow rate of the sample gas introduced into the secondary decompression chamber through the orifice becomes approximately constant.

Therefore, the gas concentration of the sample gas introduced into the secondary decompression chamber and the degree of vacuum in the secondary decompression chamber are approximately constant, and in this state the sample gas can be analyzed with a quadrupole mass detector.
It is possible to accurately detect the ion mass of a selected specific gas component contained in the sample gas.

〔Effect of the invention〕

According to the sample gas analyzer according to the present invention, as explained above, the gas flow rate of the sample gas introduced into the secondary decompression chamber through the orifice by controlling the pressure in the primary decompression chamber or the opening area of the orifice. is controlled to be substantially constant, and the gas concentration of the sample gas introduced into the secondary decompression chamber and the degree of vacuum of the secondary depressurization chamber are substantially constant, so that analysis accuracy is greatly improved.

Furthermore, there is no need to correct the measured data detected by the quadrupole mass detector using a correction coefficient, etc., and the analysis speed can be increased.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

This embodiment is a case where the present invention is applied to a sample gas analyzer that analyzes engine exhaust gas (which corresponds to sample gas).

The sample gas analyzer 1 will be explained based on FIG. 1.

The upstream end of a sample gas introduction pipe (hereinafter referred to as introduction pipe) 4 is connected to the combustion chamber 3 of the engine 2, and this introduction pipe 4
The downstream end of is introduced into the primary decompression chamber 5. Further, the upstream end of the introduction pipe 4 is provided with a control valve 6 that opens and closes the upstream end, and a solenoid 7 that drives the control valve 6 to open and close up and down.

Note that numeral 8 is an intake pipe, and numeral 9 is an exhaust pipe.

The negative pressure (degree of vacuum) inside the primary decompression chamber 5 is
A pressure sensor 10 for measuring the pressure is provided, and a vacuum pump 11 for reducing the pressure in the primary decompression chamber 5 is provided via a communication path 12.

A variable valve 13 is interposed in the middle of the communication path 12 to adjust the degree of vacuum in the primary decompression chamber 5, which is depressurized by the vacuum pump 11. Furthermore, a secondary decompression chamber 15 is provided next to the primary decompression chamber 5 with a partition plate 14 in between, and the sample gas introduced through the introduction pipe 4 is introduced into the secondary decompression chamber 15 into the partition plate 14. An orifice 16 is formed for this purpose, and the downstream end of the introduction pipe 4 is open near this orifice 16.

The secondary decompression chamber 15 includes a gas introduction valve 17 for introducing sample gas through an orifice 16, and a quadrupole mass detector 18 for measuring the ion intensity of gas components in the introduced sample gas. and valve 1 for extracting the sample gas.
9 is provided.

Further, a turbo molecular pump 20 and a vacuum pump 21 for depressurizing the secondary decompression chamber 15 to a predetermined degree of vacuum are connected to the communication path 2.
2 and 23, respectively.

As shown in FIG. 2, the four-electrode mass detector 18 includes an ion source section 24 that applies electron bombardment to gas components in a sample gas to ionize the gas components, and an ion source section 24 that converges the ionized gas components to form an ion beam. a lens system 25 forming a
There is an electrode section 26 consisting of four ronds that vibrates the ions that have entered through this lens system 25 and allows only ions with a specific charge ratio to pass through, and the ion intensity of the ions that have passed through this electrode section 26 is detected as an ion current. Secondary electron multiplier 2
7. By adjusting the voltage value applied to the electrode section 26, the ion intensity of ions with a specific charge ratio, ie, various HC ions, 02 ions, etc., is selectively detected, and this detection signal is output.

The solenoid 7, pressure sensor 10, variable valve 13,
The motors 28 and 29 that drive the vacuum pumps 11 and 21 and the motor 30 that drives the turbo molecular pump 20 are connected to a drive control section C1 of the controller C, respectively. The quadrupole mass detector 18 is the analysis control section C of the controller C.
Connected to 2.

The drive control section C1 is composed of a microcomputer, a drive circuit, etc., and controls by energizing the solenoid 7 at a predetermined timing of the exhaust stroke to drive the control valve 6 downward, and by demagnetizing the solenoid 7 after a predetermined time. Valve 6
Return to the top.

Further, the drive control unit C1 drives each motor 28, 29, and 30 based on the analysis start signal, and at the same time, the drive control unit C1 drives the primary pressure reduction based on the pressure signal from the pressure sensor 10 and a preset set pressure reduction value. The opening degree of the variable valve 13 is controlled so that the pressure in the chamber 5 is within the range between the set value and the pressure.

The analysis control section C2 supplies a drive current to the electrode section 26, the secondary electron multiplier tube 27, etc. of the quadrupole mass detector 18, and also supplies the detection signal ( The ion mass of a desired gas component is measured based on the ion intensity signal).

Next, the operation when the sample gas analyzer 1 detects the ion mass of a selected specific gas component in the exhaust gas will be explained.

When an analysis start signal is input to the drive control unit C1 with the start of analysis, the drive control unit C1 controls each motor 28, 29, 3.
0 to operate the vacuum pumps 11, 20, and 21 to reduce the pressure in the primary decompression chamber 5 and the pressure in the secondary decompression chamber 15, respectively. Then, based on the pressure signal from the pressure sensor 0, the opening degree of the variable valve 13 is controlled so that the pressure in the primary decompression chamber 5 is within the range of the set value. At this time,
The degree of vacuum in the secondary decompression chamber 15 is set to be higher than the degree of vacuum in the primary decompression chamber 5 by a predetermined value.

After the degree of vacuum in the primary decompression chamber 5 and the secondary decompression chamber 15 reach their respective set values and when the engine 2 is in the exhaust stroke, the drive control section C1 drives the solenoid 7 for a predetermined period of time to control the control valve 6 to a predetermined value. The valve is opened by driving downward for a certain amount of time. Thereby, the exhaust gas in the combustion chamber 3 is introduced into the primary decompression chamber 5 via the introduction pipe 4. At this time, the drive control section C1 controls the pressure sensor 10.
Based on the pressure signal, when the vacuum value of the primary decompression chamber 5 is lower than the set value due to the introduction of the sample gas, the opening degree of the variable valve 13 is increased, and when the vacuum value is higher than the set value, the opening degree of the variable valve 13 is increased. By narrowing down the opening degree, the degree of vacuum in the primary decompression chamber 5 is kept constant at approximately the set value while four sample gases are being supplied.

Therefore, during analysis, the difference between the degree of vacuum in the primary decompression chamber 5 and the degree of vacuum in the secondary decompression chamber 15 becomes approximately constant, so that the degree of vacuum in the primary decompression chamber 5
The gas flow rate of the sample gas introduced into the secondary decompression chamber 15 through the orifice 1G is approximately constant. Note that the sample gas remaining in the primary decompression chamber 5 is exhausted by the vacuum pump 11.

As a result, the gas concentration and degree of vacuum of the sample gas in the secondary decompression chamber 15 are approximately constant, so when analyzed by the quadruple scratch mass detector 18, the degree of ionization is approximately constant, and ions of specific gas components are Mass can be detected with high accuracy.

It is also possible to analyze intake gas or combustion gas as sample gas by driving the control valve 6 during the intake stroke or combustion stroke. In this case, the degree of vacuum in the primary decompression chamber 5 and the primary The degree of vacuum in the decompression chamber 15 is selectively set.

Next, by partially modifying the above embodiment, as shown in FIG. A sample gas analyzer 1A in which the flow rate of the sample gas introduced into the chamber 15 is kept constant will be explained. However, the points different from the previous embodiment will be explained, and since the rest is the same as the previous embodiment, the same reference numerals will be given and the explanation thereof will be omitted.

An external decompression chamber 31 is provided in place of the primary decompression chamber 5,
Inside this external decompression chamber 31, there is a hole 1 that communicates with the orifice 16.
A secondary decompression chamber 5A is provided, and the downstream end of the introduction pipe 4 is connected to the primary decompression chamber 5A.

The primary decompression chamber 5A is formed into a bag shape with a partition wall 32 of a predetermined thickness made of a stretchable material such as vinyl fluoride resin, and the primary decompression chamber 5A is connected to a three-way electromagnetic switch via a communication pipe 33. In addition to being connected to one port of the valve 34, the external pressure reduction chamber 31 is connected to the other port of the switching three-way valve 34 via a communication pipe 35, and the vacuum pump 11 is connected to the switching three-way valve 34. .

The drive control unit C3 of the controller CA is a three-way switching valve 34.
By controlling the switching, the pressure in the primary decompression chamber 5A or the external decompression chamber 31 is reduced.

Next, a description will be given of the effect of keeping the flow rate of the sample gas introduced from the primary decompression chamber 5A through the orifice 16 into the secondary decompression chamber 15 in the sample gas analyzer IA constant.

When an analysis start signal is input to the drive control unit C3 with the start of analysis, the drive control unit C3 controls each motor 28, 29, 30.
is driven to operate the vacuum pumps 11, 20, and 21 to reduce the pressure in the secondary pressure reduction chamber 15, and also to reduce the pressure in the external pressure reduction chamber 31 by switching the three-way switching valve 34.

When the pressure in the external decompression chamber 31 reaches a predetermined degree of vacuum,
The drive control unit C3 switches the three-way switching valve 34 to reduce the pressure in the primary decompression chamber 5A. Then, when the degree of vacuum in the primary decompression chamber 5A becomes between the degree of vacuum in the external decompression chamber 31, etc., the driving of the vacuum pump 11 is stopped. At this time, since the primary decompression chamber 5A and the external decompression chamber 31 have the same degree of vacuum, the partition wall 32 maintains a constant shape without being elastically deformed.

When the engine 2 is in the exhaust stroke, the drive control unit C3 drives the solenoid 7 for a predetermined period of time to drive the control valve 6 downward for a predetermined period of time to open the valve. As a result, the exhaust gas in the combustion chamber 3 is introduced into the primary decompression chamber 5A via the introduction pipe 4. The vacuum pump 11 is operated in synchronization with this gas introduction to absorb the relatively large pressure increase accompanying the introduction of the sample gas.

At this time, even if the degree of vacuum in the primary decompression chamber 5A changes with respect to the degree of vacuum in the external decompression chamber 31 when introducing the sample gas, the partition wall 32 is expandable and retractable, so that it can be adjusted according to the difference in the degree of vacuum. The partition wall 32 is elastically deformed to expand or contract the primary decompression chamber 5A. As a result, the degree of vacuum in the primary decompression chamber 5A is equal to the degree of vacuum in the decompression chamber 31, so the degree of vacuum in the primary decompression chamber 5A is
The degree of vacuum is maintained approximately constant. Thereafter, even when the gas pressure of the sample gas changes, the partition wall 32 freely deforms elastically in accordance with the change in gas pressure, and the volume of the fire source pressure chamber 5A expands or contracts. Next, the degree of vacuum in the decompression chamber 5A is kept substantially constant.

Therefore, from the primary decompression chamber 5A of constant pressure to the orifice 16
The flow rate of the sample gas introduced into the secondary decompression chamber 15 at a constant pressure through the secondary decompression chamber 15 becomes approximately constant. As a result, the gas concentration and degree of vacuum of the sample gas in the secondary decompression chamber 15 become approximately constant.
When analyzed by the quadrupole mass detector 18, the degree of ionization becomes constant, and the mass of a specific gas component can be detected with high accuracy.

It is also possible to form the partition wall 32 into a bag-like shape using a film-like material made of an expandable material. In this case, the degree of vacuum in the external decompression chamber 31 is set higher than the degree of vacuum in the primary decompression chamber 5A. When used with tension acting on the partition wall 32, the partition wall 32 can provide a pressure regulating effect against fluctuations in pressure within the primary decompression chamber 5A.

The above embodiment is partially modified, and the opening degree of the orifice 16 is adjusted as shown in FIG. A sample gas analyzer IB that maintains a constant flow rate will be described.

However, the points different from the previous embodiment will be explained, and since the rest is the same as the previous embodiment, the same reference numerals will be given and the explanation thereof will be omitted.

As shown in FIGS. 4 and 5, the partition plate 1 of the primary decompression chamber 5
A disk 36 whose center position is approximately the orifice 16 formed in the orifice 16 is fixed to the partition plate 14, and this disk 36 has a disk 36 for guiding an adjustment plate 37 that adjusts the opening degree (opening area) of the orifice 16. A long hole 36a is formed, and this adjustment plate 3
At the lower end of 7, an adjustment plate 37 is moved up and down to open orifice 1.
A glue near solenoid 38 is connected to adjust the opening degree of the valve 6. Incidentally, the disk 36, the adjustment plate 37, and the linear solenoid 38 constitute an orifice opening adjustment mechanism 39.

A pressure sensor 40 is provided in the combustion chamber 3 of the engine 2,
The pressure sensor 40 and the linear solenoid 38 are each connected to the drive control section c4 of the controller CB.

The drive control unit C4 drives the linear solenoid 38 of the orifice opening adjustment mechanism 39 to adjust the opening of the orifice 16 when the pressure in the combustion chamber 3 rises above a set value based on the pressure signal from the pressure sensor 4o. The opening of the orifice 16 is increased according to the degree of the pressure drop by driving the near solenoid 38 and increasing the opening degree of the orifice 16 when the pressure decreases below a set value. Incidentally, in order to keep the gas flow rate of the sample gas passing through the orifice 16 substantially constant, the opening degree characteristic indicating the correlation between the pressure signal and the opening degree of the orifice 16 is stored in advance in the storage section of the drive control section c4. There is.

Next, a description will be given of the effect of keeping the flow rate of the sample gas introduced from the primary decompression chamber 5 into the secondary decompression chamber 15 via the orifice 16 in the sample gas analyzer 21B constant.

When an analysis start signal is input to the drive control unit C4 with the start of analysis, the drive control unit C4 controls each motor 28, 29, 30.
The vacuum pumps 11, 20, and 21 are operated to reduce the pressure in the primary decompression chamber 5 and the secondary decompression chamber 15 to the respective set vacuum degrees. After the degree of vacuum in the primary decompression chamber 5 and the secondary decompression chamber 15 reach their respective set values, during the exhaust stroke of the engine 2,
The drive control unit C4 drives the solenoid 7 for a predetermined period of time to drive the control valve 6 downward and open it. As a result, the combustion chamber 3
The exhaust gas inside is introduced into the primary decompression chamber 5 via the introduction pipe 4. At this time, the drive control unit C4 drives the glide solenoid 38 of the orifice opening adjustment mechanism 39 based on the pressure signal of the pressure sensor 40 and the predetermined opening characteristic to adjust the opening of the orifice 16. .

Therefore, when the gas pressure of the sample gas is high, the opening degree of the orifice 16 is narrowed down by the orifice opening degree adjustment mechanism 39, and when the gas pressure is low, the opening degree of the orifice 16 is increased, so that the sample passing through the orifice 16 is The gas flow rate of the gas becomes approximately constant. As a result, the gas concentration and degree of vacuum of the sample gas in the two-fire source pressure chamber 5 are approximately constant, so the degree of ionization is constant when analyzed by the quadrupole mass detector 18, and specific data can be detected with high precision. The mass of gas components can be detected.

As explained above, when introducing the sample gas, the degree of vacuum in the primary decompression chambers 5 and 5A is kept approximately constant, and the degree of opening of the orifice 16 is controlled by the orifice degree adjustment mechanism 39. Therefore, the flow rate of the sample gas passing through the orifice 16 becomes approximately constant, the degree of vacuum in the secondary decompression chamber 15 is stabilized, and the degree of ionization of a specific gas component is stabilized when analyzed by the quadrupole mass detector 18. However, the accuracy of analysis by the quadrupole mass detector 18 is greatly improved.

Further, there is no need to correct the actual measurement data detected by the quadrupole mass detector 18 using a correction coefficient, etc., and the analysis speed can be increased.

It goes without saying that the sample gas analyzer 1, IA, and IB according to the present invention can analyze various gases used in research, environmental gases in the living environment, etc. as sample gases.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention. Figure 1 is a schematic diagram of a sample gas analyzer, Figure 2 is a schematic diagram of a quadrupole mass detector, and Figures 3 and 4 are side views of each side. 1 is a diagram corresponding to FIG. 1 of the sample gas analyzer according to the embodiment, FIG. 5 is a schematic diagram of the orifice opening adjustment mechanism, and FIG. 6 is a schematic diagram of the sample gas analyzer according to the prior art. 1・IA・IB・・Sample gas analyzer, 4・・Sample gas introduction tube, 5・5A・・Primary decompression chamber, 10・40・・
Pressure sensor, 11・21・・Vacuum pump, 15・
・Secondary decompression chamber, 16...orifice, 18...
Quadrupole mass detector, 39... Orifice opening adjustment mechanism, C1, C3, C4... Drive control unit.

Claims (1)

[Claims] (1) A primary decompression chamber into which a sample gas introduction pipe is introduced, a secondary decompression chamber communicated with the primary decompression chamber through an orifice, and a quadrupole mass detection device provided in the secondary decompression chamber. In the sample gas analyzer equipped with A sample gas analyzer characterized by being provided with a gas flow rate control means for controlling area.